Dyes known as dyes or pigments are widely utilized in various applications including coloring materials for fibers, colorants for resins and paints, image forming materials in photography, printing, copying machines and printers and light-absorption materials for color filters. Recently, various image forming dyes for color hard-copies employing ink jet technology, electrophotography technology, silver salt photography technology and thermal transfer technology were disclosed. In addition, together with the accelerating progress of electronic imaging, demand for dyes for photorecording media utilizing a solid image pick-up tube, dyes for filters for color liquid crystal television and semiconductor lasers has been increased. Therefore, utilizing field of dyes have been extended.
Among the above-mentioned dyes, the thermal transfer recording has advantage in that operation and maintenance is easy, downsizing of the associated apparatus and further cost reduction is possible, and its running cost is inexpensive. In order to improve stability, specifically fixing property and light fastness, of an image obtained by the thermal transfer recording, a thermal recording material and an image forming method employing a chelatable thermo-diffusion dye (hereinafter, referred to as "chelate dye") have been reported. For example, they are reported in Japanese Patent Publication Open to Public Inspection (hereinafter, referred to as Japanese Patent O.P.I. Publication) Nos. 78893/1984, 10349/1984 and 2398/1985. The chelate dyes disclosed in the above-mentioned patent applications are metal chelate dyes wherein azo dyes are bidentate- or tridentate-cordinated with metal ions as a ligand. An image formed by the use of the above-mentioned chelate dyes is excellent in terms of light fastness and fixing property. However, it is not satisfactory in terms of sensitivity of thermal transfer recording material nor of the storage stability of the material itself. Therefore, further improvement has been demanded. Since hue change of the azo dye and that of the chelate dye after chelating is formed are remarkable, undesired secondary absorption occurs when chelating reaction, when an image is formed, is insufficient. In addition, the formed chelate dye itself is irregularly absorbed. Accordingly, when a full color image is obtained, further improvement in terms of color reproduction is demanded.
In addition, when the above-mentioned dye is used as an ink for ink jet printing, there are the following requirements: (a) it must be compatible with various recording methods (including (1) a method wherein solution drops are pressed and emitted by means of electromechanical conversion by means of Piezo element, (2) a method wherein solution drops are pressed and emitted by generating bubbles by means of electricity-heat conversion and (3) a method wherein solution drops are suctioned and emitted by means of static electricity), (b) having high recording density and favorable color tone, (c) being excellent in terms of image fastness to light, heat and moisture, (d) fixing fastness on the recording medium so that no blotting occurs after recording, (e) being excellent in terms of storage stability as an ink, (f) there are no problems in terms of safety such as toxicity and impressing and (g) it is inexpensive. From the above-mentioned viewpoints, various solutions for ink jet method are disclosed and studied. However, recording solutions satisfying many of the above-mentioned requirements concurrently are extremely limited. In color image recording employing a yellow, magenta, cyan and black color, dyes and pigments having conventional C.I. numbers described in the C.I. index have widely been studied. Those employing xanthene-containing water-solubilizing dyes such as Acid Red 52 and azo-containing water-solubilizing dyes such as Direct Red are known. However, the former has problems in terms of fastness such as light fastness and the latter has problems in terms of spectral absorption properties regarding color reproducibility, for example, lacking color tone sharpness.
Further, a case when the above-mentioned dye is used in color toner will now be discussed. In a color copier or a color printer utilizing an electrophotographic system, toner wherein a colorant is dispersed in resin particles or toner in which colorant is adhered on the surface of resin particles is ordinarily employed. It is difficult to achieve excellent effects when a method wherein a colorant is adhered on the surface of resin since it is coloring only on the surface of the resin. In addition, since the colorant is removed from the resin, charging performance changes. In addition, another problem occurs in that the surface of the fixing rollers is contaminated. Therefore, toners in which the colorant is dispersed in side the particles are widely employed. As performances required for such color toners, color reproducibility, image penetrability and light fastness in an Over Head Projector (hereinafter, referred to as "OHP") are cited. Toners in which a pigment is dispersed inside particles as a colorant are disclosed in Japanese Patent O.P.I. Publications Nos. 157051/1987, 255956/1987 and 118715/1994. Though these toners are excellent in terms of light fastness, they easily coagulate since they are insoluble. Therefore, they result in reduction in transmissivity and hue change of transmitting colors. In addition, toners wherein a dye is used as a colorant are disclosed in Japanese Patent O.P.I. Publications Nos. 276161/1991, 207274/1990 and 207273/1990. To the contrary, these toners have transmissivity so that they have problems in terms of light fastness, though there is no hue change.
It is desired that the above-mentioned dyes commonly have the following characteristics. Namely, they have preferable hue in terms of color reproduction, they have the most suitable spectral absorption characteristics, their image fastness to light, heat and moisture and chemical fastness is favorable. Further, their mol light absorption coefficient is large.